(Adapted from the application's abstract) Impaired energy metabolism due to hyperoxic exposure may have important negative consequences for lung growth, development and function in the newborn such as the poorly developed, scarred lungs of bronchopulmonary dysplasia. The possibility that energy metabolism is seriously inhibited by normobaric hyperoxia has been an issue of considerable controversy. However, the recent identification of the critical tricarboxylic acid cycle enzyme aconitase as a target which is rapidly and potently inhibited by hyperoxia provides one example of such an impairment which may have devastating effects on lung growth and function. It is hypothesized that inactivation of the critical tricarboxylic acid cycle enzyme aconitase by hyperoxia is a key event which inhibits energy (ATP) production, and , consequently, lung cell growth and function in the premature newborn. Nitric oxide also could play a contributory role in this process. Further, it is proposed that this process may be exaggerated in the premature due to a deficiency of important lung antioxidant defenses. In addition, it is suggested that interventions which either inhibit aconitase inactivation or potentiate its re-activation or which facilitate energy production through its alternative mechanism, will restore lung cell growth and function. To test these hypothesis, alveolar epithelial cells from late gestation fetal rat grown on matrix, and, in some studies, co-cultured in the presence of living matrix cells on floating filters, or fetal lung explants, will be utilized. The effects of inhibition of aconitase both by hyperoxia and by the potent specific inhibitor fluorocitrate on energy production, growth, cell work such as surfactant protein expression and lipid production, and expression of epithelium-derived growth factors critical in pulmonary vascular development such as vascular endothelial growth factor (VEGF) all will be assessed. Nuclear magnetic resonance and other analytical biochemical techniques will be used to make real-time determinations of energy and intermediary metabolites during ongoing exposure to hyperoxia or flurocitrate. In bovine fetal pulmonary vascular endothelial cells, the effect of aconitase inhibition on cell energy status, growth, and growth- related function (expression of VEGF receptors) will be assessed. Further, the sensitivity of other cell types of the vascular wall, smooth muscle and fibroblast, to energy impairment and growth inhibition due to aconitase inhibition will be compared. Based on these studies, antioxidant interventions which may decrease aconitase inactivation by hyperoxia, or increase it re-activation, will be evaluated for potential palliative effects. Through novel approaches, these studies will provide new information about the mechanisms by which hyperoxia impairs energy metabolism in the lung and alters pulmonary vascular growth and development. In addition, palliative therapies could be developed as a result.